Previous studies of bovine nasal cartilage have led to a hypothesis for the macromolecular organization of cartilage ground substance. Since the concepts from which this hypothesis was formulated were derived entirely from studies of bovine nasal cartilage proteinpolysaccharides, proteinpolysaccharides from bovine articular cartilage are being studied to determine whether these concepts and the hypothesis are applicable to other cartilages. Proteinpolysaccharide basic structural unit and aggregate forms from bovine articular cartilage have been prepared and are being chemically and physically characterized. One-third of the proteinpolysaccharide of bovine articular cartilage is non-covalently bound to a protein different from glycoprotein link (GPL) in the cartilage matrix and resists extraction by one agent known to dissociate aggregate (3M MgCl2) but is solublized by another (4M guanidinium chloride). Following extraction of proteinpolysaccharide and this protein with 4M guanidinium chloride, high molecular weight complexes between proteinpolysaccharide and this protein form in associative solvents of low electrolyte concentration, which are dissociable by guanidinium chloride but not by 3M MgCl2. This protein is now to be isolated, its binding to proteoglycan subunit (PGS) studied by analytical ultracentrifugation, and the properties of the high molecular weight complex formed contrasted with those of aggregates formed from PGS and GPL.